A research team from China has proposed a transparent smart radiation device (TSRD) for efficient thermal management of solar cells on spacecraft, which are exposed to harsh environmental conditions, especially extreme thermal fluctuations, which can affect device performance and light absorption.
The TSRD, which can be applied to cells as a coating, uses a thermochromic material that changes how much heat it releases depending on the temperature. “Our research presents a multi-dimensional breakthrough, as we introduce a novel TSRD which resolves the long-standing challenge of balancing high visual transparency with effective thermal radiation control,” corresponding author Xiaohu Wu told pv magazine.
The thermochromic material used by the team was vanadium dioxide (VO2). This compound transitions from an insulating state to a metallic state at a phase transition temperature of 68 C, which can determine a dramatic change in its optical properties. Therefore, a transparent substrate was deemed necessary.
The team tested three substrates in a MATLAB simulation: Single-layer indium tin oxide (ITO), single-layer silver (Ag), and a structure of ITO/Ag/ITO. In between the substrate layer and the VO2, the academics placed a protective layer of barium fluoride (BaF₂). Per their optimization, the VO2 had a thickness of 0.015 μm, and the BaF₂ had a thickness of 1.5 μm in all cases. The optimized single ITO thickness was 0.26 μm, the single Ag was 0.003 μm, and the combined layer included Ag of 0.003 μm with ITO of 0.01 μm from each side.
“Balancing the performance of TSRD across various spectral bands, the VO2/BaF2/ITO/Ag/ITO structure demonstrates superior performance among the three cases,” the scientists said, noting that the coating was able to achieve transmission of 0.8 and 0.72 in the visible spectrum under high- and low-temperature conditions, respectively, a solar absorption of only 0.16, and an emission modulation of up to 0.51 in the infrared band.
Furthermore, they found that the VO2/BaF2/ITO device achieved transmission of 0.69 and 0.63 under high- and low-temperature conditions, respectively. Solar absorption was found at 0.28, and emission modulation was 0.44. In the case VO2/BaF2/Ag, the results were 0.77, 0.70, 0.15, and 0.52, respectively. “Moreover, the addition of a lossless dielectric layer as a protective coating not only preserves the excellent performance of the TSRD but also holds the potential to enhance its durability and lifespan,” the academic added.
“For experimental validation and engineering applications, we plan to prepare high-quality TSRD samples and conduct performance tests under extreme conditions simulating the space environment,” Wu said. “By comparing experimental data with theoretical models, we aim to assess TSRD's stability, reliability, and long-term performance in real space environments, providing an experimental foundation for its practical use in spacecraft thermal management systems.”
The novel technique was presented in “Transparent smart radiation device for efficient thermal management of spacecraft solar cells,” published in Case Studies in Thermal Engineering. Scientists from China’s Northwestern Polytechnical University and the Shandong Institute of Advanced Technology contributed to the research.
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